Willingness-to-pay for a hypothetical Ebola vaccine in Indonesia: A cross-sectional study in Aceh

Study design and setting

Approximately 16 months after the Ministry of Health of the Republic of Indonesia raised an alert for EVD in Indonesia, a cross-sectional study was conducted to assess acceptance and WTP for a hypothetical Ebola vaccine among family members of patients with any illness admitted to eight health facilities (hospitals or Community Health Centres [Puskesmas]) in four regencies (Nagan Raya, Aceh Selatan, Langsa and Banda Aceh) of Aceh province from 1 August to 30 December 2015. The study was conducted in. Aceh is located in the westernmost part of the Indonesian archipelago with a total population approximately 4,906,800 in 2014¹⁷.

Study participants, sampling and sample size

Study participants were patients’ family members who visited infection and non-infection outpatient departments. Based on the population size of Aceh in 2014, the minimum sample size required was 385¹⁸. To recruit the samples, four regencies were selected randomly, and both urban and suburban areas were included. The number of participants from each study site was gathered proportionally to the size of regency’s population. To avoid repetitive field visits and to minimize the study design effect, the number of participants was increased for each study site. Family members who had resided in the specified regency for more than 3 months, were ≥17 years old, and were able to communicate in Bahasa Indonesia (the national language) were considered to be eligible for inclusion.

Study instrument

To facilitate the interviews a set of a structured questionnaire, adapted from previous studies^19,20, was used. Prior to use in the actual study, a pilot study was conducted to measure reliability of questionnaires among 25 participants in Lhokseumawe regency. For this pilot study, a Cronbach’s alpha score of ≥0.7 was considered good internal consistency. Edits were made to the questionnaire based on findings from the pilot study; the questionnaire is available in Indonesian and English as Extended data²¹.

Study variables

Response variable. The response variable was WTP for a hypothetical Ebola vaccine. Prior to assessing their WTP, participants were provided with an introduction to the Ebola disease including the symptoms and modes of transmission. They were also informed of the following points: (a) infected patients need to be isolated and health care workers need to use special protection equipment while providing healthcare to the patients; (b) currently there is no available treatment for EVD; (c) the mortality rate of EVD is up to 90%; and (d) an Ebola vaccine would be safe and protective against EVD.

To assess the amount of money that participants would be willing to pay for a hypothetical Ebola vaccine, participants were asked whether they would be willing to pay for the vaccine using a list of Ebola vaccine prices: Indonesian Rupiah (IDR) 5.000, 10,000, 17.500, 37.500, 87.500, 150.000, and 300.000 (equivalent to US$ 0.37, 1.29, 2.78, 4.63, 6.48, 11.12, and 22.24). The possible responses were “very likely”, “likely”, “undecided”, “unlikely” or “very unlikely”. The WTP was defined as the highest price the participants said they were still “very likely” or “likely” willing to pay.

Explanatory variables. Sociodemographic data: Sociodemographic factors such as age, gender, educational attainment, type of occupation, marital status, monthly income and urbanicity were collected from participants. The date of birth was recorded, converted into actual age and then collapsed into three groups. Educational attainment, defined as the highest level of formal education completed by respondents, was grouped into four groups. Participants were grouped into five types of occupation: (a) farmer; (b) private sector employee; (c) housewife; (d) entrepreneur (owned a small-scale business, or traders in a market); and (e) civil servant. Monthly income was grouped into: (a) less than 1 million Indonesian Rupiah (IDR) (equivalent to US$ 74.1); (b) 1 –2 million IDR (equivalent to US$ 74.1 - US$ 148.2); and (c) more than 2 million IDR (equivalent to US$ 148.2). Urbanicity included cities and suburbs.

Socioeconomic status (SES): SES was assessed based on 15 household assets owned by participants such as radio, landline phone, refrigerator, motorcycles, car, other electronics and house characteristics. Details of the full list of the household assets have been published previously^20,22. The ownership of those assets was used to construct an asset index based on principal component analysis²³. SES classified into three tertiles, with the 1^st tertile the poorest and the 3^rd tertile the wealthiest.

Attitude towards vaccination practice: To measure attitude towards vaccination practice, five questions adopted from a previous study²⁰ was used. The questions included the attitude towards the safety and importance of vaccines, and previous experiences regarding vaccination practices. Participants responded to each statement on a five-point Likert-like scale ranging from “1=strongly disagree” to “5=strongly agree” with a higher score indicating a more positive attitude. The summed scores for this domain ranged from 5 to 25. Participants were classified as having a ”good” or ”poor” attitude based on a 75% cut-off point of the maximum score achieved by participants.

Knowledge regarding Ebola: To assess knowledge regarding Ebola, a set of six questions on transmission and prevention methods of EVD, adapted from a previous study¹⁹, was used. Each valid response was given a score of one, whereas an incorrect response was given a score of zero. The summed scores for this domain ranged from 0 to 6, and knowledge of each participant was also classified into ”good” or ”poor” based on a 75% cut-off point.

Data analysis

To assess the relationship between explanatory variables and WTP, a multivariable linear regression model was employed^24,25. Various diagnostic assessments were used to check how well the data met the assumptions of linear regression. The variance inflation factor (VIF)²⁶, Glejser test²⁷ and Kolmogorov-Smirnov test²⁸ were employed to assess multicollinearity, heteroscedasticity and residual normality of the data, respectively. A VIF value of lower than 10 was used to define no multicollinearity between variables. A P-value greater than 0.05 in the Glejser test, and Kolmogorov-Smirnov test was applied to indicate no heteroscedasticity, and normal distribution of residuals, respectively²⁴.

Initial assessment indicated that the data violated all three assumptions and WTP values were then transformed using a natural logarithm function (Ln). After transformation, data showed better adherence to assumptions and therefore the transformed WTP values were used in linear regression model. In the initial multivariable model, all explanatory variables were included. Then, all explanatory variables that had P > 0.25 in this model were excluded from final linear regression model²⁹. Significance in the final model was assessed at an alpha level of 0.05. All associations between an explanatory factor and WTP were interpreted in relation to a reference category.

Because the outcome had been log-transformed, the mean estimated WTP in US$ and its 95% CI were calculated as $\text{Exp}(\text{X}\widehat{\beta }+{\widehat{\sigma }}^2/2)$ where $\widehat{\beta }$ was the estimated regression coefficients (B) and ${\widehat{\sigma }}^2$ was the mean squared error (MSE) of the multivariate model^24,30,31. All analyses were performed using SPSS (version 15, Chicago, USA).

Ethical approval

The protocol of this study was approved by Institutional Review Board of the School of Medicine, Universitas Syiah Kuala, Banda Aceh, Indonesia (Approval 315/KE/FK/2015). Prior to enrolment, the aims of the study were explained to the participants and they signed written consent forms. Participation in this study was voluntary and participants received no financial compensation.

Participants’ characteristics

In this study, 500 participants were approached, all agreed to participate, but 76 were excluded due to incomplete data. Among those with completed data (424 or 84.8%), approximately 74% (311/424) of participants would accept an Ebola vaccine. There were 288 participants (92.6%, 288/311, of those who would accept an Ebola vaccine, or 67.9%, 288/424, of all participants with completed data), willing to pay for Ebola vaccine. The characteristics of the participants who were willing to pay for Ebola vaccine are presented in Table 1.

More than half (51.0%) of those who willing to pay for the vaccine were aged 30–44 years old, and 52.4% were female. A majority (75.7%) of them had finished their senior high school (year 12) and none of them had no formal education. The most frequent type of occupation was farmer, followed by entrepreneur, housewife, civil servant and private employee. A vast majority (96.5%) of the respondents who willing to pay were married and approximately 44% of the them were living under the poverty line, i.e. <1 million IDR (equivalent to US$74.1). Overall, 52.1% of them had good attitude towards vaccination and almost 70% had poor knowledge about transmission and prevention of EVD.

WTP for an Ebola vaccine

Among 288 participants who were willing to pay for Ebola vaccine, 114 (39.6%) of them expressed their WTP at US$ 1.29 and this decreased to 28.1%, 14.6% and 3.1% as the price for Ebola vaccine increased to US$2.78, US$4.63, and US$6.48, respectively (Figure 1). Only 7 out of 288 respondents agreed to pay the highest price (US$22.24). The mean of WTP was US$2.08 (95% CI: 1.75-2.42).

Figure 1. Relationship between the presented vaccine price and proportion of participants who were willing to pay for an Ebola vaccine in Aceh, Indonesia.

Only those who were willing to pay for Ebola vaccine were included in this analysis.

Factors associated with WTP for an Ebola vaccine

The initial multivariable model showed that age, educational attainment, type of occupation, marital status, type of residence and having good knowledge of Ebola were associated with WTP with a P-value under 0.25. (Table 1). The final multivariable model indicated that age, educational attainment, type of occupation, marital status and urbanicity were significantly associated with WTP (Table 2). Knowledge of Ebola had no association with WTP. Compared to the youngest age group (17–29-year-olds), participants who were between 30–44 years old and those older than 45 years had lower WTP, at approximately US$ 1. Respondents who finished senior high school (year 12) and graduated from university had higher WTP – approximately US$1.7 and US$2.3, respectively, compared to those who had an education less than junior high school (year 9). Compared to farmers, participants who were working as employees in private companies, entrepreneurs and civil servants were willing to pay US$2.6, US$1.8 and US$2.3 more, respectively. In addition, this study found that participants who were married and those who were living in the city had lower WTP compared to unmarried participants and those who were living in the suburbs (Table 2).

Underlying data

Figshare: Willingness-to-pay for a hypothetical Ebola vaccine in Indonesia: A cross-sectional study in Aceh. https://doi.org/10.6084/m9.figshare.9256037³².

This project contains answers given to each question by each participant.

Extended data

Figshare: Willingness-to-pay for a hypothetical Ebola vaccine in Indonesia: A cross-sectional study in Aceh (Questionnaire). https://doi.org/10.6084/m9.figshare.9293378.v1²¹.

This project contains the questionnaire in Indonesian (original) and English.

Data are available under the terms of the Creative Commons Attribution 4.0 International license (CC-BY 4.0).